<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>判断是否是闰年</title>
</head>

<body>
    <script>
        var n = parseInt(prompt('请输入一个年份'));
        if (n == isNaN) {
            alert('请输入正确的年份');

        } else {
            alert(year(n));
        }

        function year(n) {
            if (n % 4 == 0 && n % 100 != 0 || n % 400 == 0) {
                return '输入的年份为闰年';
            } else {
                return '输入年份为平年';
            }
        }
    </script>
</body>

</html>